Currently, nearly all musicians who play live or record music incorporate electronic effects units in their performance in some way. Such electronic effects units can be used to enhance the sound possibilities of any instrument type, including acoustic and electric string instruments, wind instruments, percussion instruments and vocals. The most common users of such effects units are guitarists (electric guitar in particular) and there is a large variety of electronic effects devices available for guitars.
In most cases, effects units for guitar are designed as separately powered devices, activated by foot-operated switches or pedals, and are placed in the signal path between the instrument and the amplification or recording equipment.
Most stringed and fretted instruments, including the electric and acoustic guitar have a certain set of limitations, due to the physical nature of the strings, and how notes are formed.
First of all, a plucked or bowed string can only produce one fundamental note at a time and the note's tonality is determined by where the string is pressed on the fret-board. Therefore—a six-string guitar allows only six notes to be played at once. For comparison—wind instruments such as saxophone, trumpet, etc., usually produce only one tone at a time whereas a grand piano can produce 88 notes simultaneously if all keys are struck at once.
Secondly, the natural decay-length of the sound produced by the strings (chords or individual notes) is pre-determined by the physical characteristics of each particular instrument type, string gauge, playing volume, resonator size etc. Sounds produced by strings (both fretted and unfretted) can also get muted easily, as soon as they are touched while a note is ringing. Also, any fretted note requires constant physical contact between the string and the fret-board in order to keep ringing—as soon as the contact is interrupted, when the string is released from the fret-board, the note ceases to ring (sound dies).
Acoustic pianos typically offer a built-in Sostenuto pedal, which can be used to significantly extend the decay length of all notes played and achieve long ringing notes and chords with only a short tap of the keys. This function is made possible with the use of built-in string dampers, which are mechanically lifted away from the piano's strings when the Sostenuto pedal is pressed, thus letting notes ring out in their full length, even after the keys are released.
Thus pianists can play rhythm and harmony parts with their left hand, while playing melodies on top with the right hand, while guitarists are usually limited to playing only one musical part at a time. In some cases it is possible to compose such song arrangements which combine chords and melody; however this requires mastering a highly complex playing technique that also leaves little space for improvisation. In most cases, guitarists are forced to constantly switch between playing chords and solo/melodic parts. In situations where the guitar is the only harmonic instrument (in small bands or when playing unaccompanied) this can be a real limiting factor.
In response to these limitations—a separate class of digital and electronic effects units have been introduced to give guitarists, as well as other musicians, the ability to layer the signal produced by the instrument—play multiple musical parts at once—and in some cases to accompany themselves.
The following section discusses the most commonly used devices and their characteristics, i.e. existing solutions and their shortcomings.
Delay units: Delay effects units are used to expand the instrument's sound, by adding a repeating, decaying echo to the signal output. The instrument's input signal is being constantly recorded onto an audio storage medium, and then played back rhythmically at a certain tempo set by the musician; the number of playback times and the decay in the playback volume are also variable.
Delay effects units are some of the most commonly-used effects for guitars, vocals and other instruments, however they are not useful for separating harmonic/rhythm parts from melodies/solos, since they affect both signals and produce very distinct continuous rhythmical patterns.
Looping systems: Looping units are usually foot-controlled devices that allow musicians to perform multi-track recording in real-time and play different tracks in a continuous loop. For example, by recording a rhythmic chord and harmony part on a separate track and playing it back instantly, one can proceed playing a new musical part on top—that way creating multiple layers of sounds and performing more detailed musical arrangements. This system however requires sequential input of audio data, and also it limits the musical performance to a specific predetermined loop-length, set by the user—for example—4 bars or 8 bars etc.
Synthesizer units: Certain synthesizer units are able to mimic analog instruments in real-time create and continuous tones, based on the tonality of notes/chords being played. In some devices upon receiving a control signal, the pitch and timbre of the note/chord that is being played at that particular moment is measured and the device uses oscillators and envelope filters to reproduce an approximation of that sound.
Such effects units are versatile and can be played dynamically, but in most cases they sound different from real instruments, since the output is generated with oscillators and not actual audio samples.
The purpose of the invention is to create an electronic effects unit that is able to “stretch out” any complex audio signal (chords, intervals etc.) thus offering musicians, primarily guitarists, an alternative way of playing multiple musical parts simultaneously, extending the length of notes—a principle similar to the Sostenuto pedal found on most acoustic pianos.